No member of the Saturn rocket family ever killed an astronaut. Two Saturn rocket designs were rated as safe enough to launch humans into space: the two-stage Saturn IB, which flew nine times between February 1966 and July 1975, and the Saturn V, which flew 12 times with three stages between November 1967 and December 1972, and once with two stages in May 1973. The 200-foot-tall Saturn IB flew five times with astronauts on board (Apollo 7, Skylab missions 2, 3, and 4, and the Apollo-Soyuz Test Project), while the 363-foot-tall Saturn V launched astronauts 10 times (Apollo missions 8 through 17).
Although man-rated, Saturn V rockets experienced four close calls. The first occurred on 4 April 1968, during the unmanned Apollo 6 test flight, when instability in the rocket's fiery exhaust plume produced violent fore-and-aft shaking known as "pogo." Two of the five J-2 engines in the rocket's S-II second stage shut down and pieces broke away from the streamlined shroud linking the Apollo Command and Service Module (CSM) to its S-IVB third stage. The S-IVB's single J-2 engine underperformed, placing the stage and CSM into a lopsided orbit, then refused to restart. Had the Apollo 6 CSM carried astronauts, pogo might have injured them; even if they had reached orbit unscathed, the S-IVB engine failure would have scrubbed their moon mission.
Apollo 12 experienced an even more perilous ascent. Following launch in a rainstorm on 14 November 1969, lightning struck its Saturn V 36.5 and 52 seconds after liftoff. The lightning strikes knocked the Apollo 12 CSM Yankee Clipper's three electricity-generating fuel cells offline, along with its computer and most other electrical systems. The Saturn V's IBM-built Instrument Unit - its ring-shaped electronic brain, located atop its S-IVB third stage - soldiered on without a hiccup, however, safely guiding the giant rocket into orbit. The Apollo 12 crew of Pete Conrad, Alan Bean, and Dick Gordon carried out a successful lunar landing mission and returned to Earth on 24 November.
The third Saturn V close call saw the return of pogo. During ascent to orbit on 11 April 1970, the middle engine of the Apollo 13 Saturn V S-II stage began to rapidly oscillate fore and aft, then shut down two minutes early. The four remaining engines burned for longer than planned to compensate. Apollo 13 astronauts Jim Lovell, Fred Haise, and Jack Swigert subsequently left Earth orbit for the moon, but an oxygen tank explosion in their CSM, the Odyssey, scrubbed their moon landing. They used their Lunar Module (LM) moon lander, the Aquarius, as a lifeboat and returned safely to Earth on 17 April.
The final Saturn V to fly, intended originally for Apollo 20 but launched unmanned with the Skylab Orbital Workshop (OWS) on top in place of an S-IVB stage and the Apollo CSM and LM spacecraft, survived a close call on 14 May 1973. A design flaw caused Skylab's meteoroid shield to tear loose 63 seconds into the flight. As the disintegrating shield tumbled down the length of the accelerating rocket, it tore at least one hole in the interstage adapter that linked the OWS to the S-II second stage and apparently damaged the system for separating the ring-shaped interstage adapter that linked the S-II with the S-IC first stage. This meant that the 18-foot-long adapter did not separate from the S-II three minutes and 11 seconds into the flight as planned. The S-II stage dutifully hauled its unplanned five-ton cargo into Earth orbit.
Apollo 12 might easily have ended in a Launch Escape System (LES) abort. The image at the top of this post shows the LES in action during Pad Abort Test-2 on 29 June 1965. The LES was a 33-foot-tall tower containing three solid-fueled rocket motors. It stood atop the Boost Protective Cover (BPC), a conical shell that covered the CSM's Command Module (CM). The CM contained the crew during launch and ascent to orbit. In the event of a catastrophic launch vehicle failure on the launch pad or during the first three minutes of ascent, the LES would pull the BPC and CM free of the Saturn rocket.
As the LES expended its solid propellant, the CM would detach from the BPC. For an abort from the launch pad, parachutes in the CM's nose would deploy immediately after BPC separation; for aborts at higher altitudes and farther downrange, the CM would turn its bowl-shaped heatshield forward to protect it from reentry heating and to shed velocity prior to parachute deployment. In most cases, the CM would splash down in the Atlantic following an LES abort.
In August 1965, R. High and R. Fletcher, engineers at NASA's Manned Spacecraft Center in Houston, Texas, calculated the characteristics of Saturn IB and Saturn V launch pad explosions to aid LES development. Of particular concern, they explained, was the damage an explosion fireball's heat might do to the CM's nylon main parachutes. In their report they did not, however, reach specific conclusions about parachute heat damage.
High and Fletcher found that calculating the characteristics of launch pad failures was not an exact science, in large part because there were so many variables to be taken into account, and also because no rocket as large as the Saturn V had ever exploded. They explained that "many of the [fireball] parameters may defy an accurate theoretical treatment."
For their analysis, they assumed that all propellants in the exploding rocket would contribute to forming a fireball. This would occur, they explained, because "large overpressures from detonations and the intense heat from both detonations and burning would cause failure of any propellant tanks not initially involved." If a Saturn V exploded on the pad at launch, 5.492 million pounds of RP-1 refined kerosene, liquid oxygen (LOX), and liquid hydrogen would contribute to its fireball. For a Saturn IB pad explosion, 1.11 million pounds of RP-1, LOX, and liquid hydrogen would fuel its fireball.
High and Fletcher wrote that the fireball from a Saturn rocket launch pad failure would expand in a "nearly fixed location." For the Saturn V, the fireball would expand to a diameter of 1408 feet. The Saturn IB fireball would expand to 844 feet. The fireballs would thus completely engulf the Saturn launch pads. For both rockets, fireball surface temperature would attain 2500° Fahrenheit, and heat would be felt up to a mile from the launch pad.
A fireball would begin to rise when it reached its maximum diameter. Fireball ascent would commence about 20 seconds after a Saturn V launch pad explosion and about 10 seconds after a Saturn IB explosion, High and Fletcher calculated. The Saturn V fireball would reach an altitude of about 300 feet in 15 seconds, while the Saturn IB fireball would climb 300 feet in 11 seconds. The Saturn V fireball would persist at its maximum diameter for 34 seconds, while the Saturn IB fireball would last for 20 seconds. The fireball would then begin to cool and dissipate.
Though they assumed for their calculations that all propellants in an exploding Saturn rocket would contribute to its fireball, High and Fletcher wrote that some would likely be "spilled on the ground, creating residual pools which [would] burn for relatively long periods of time." This was, they judged, especially likely if a launch pad failure began with the rupture of the fuel tank in the Saturn V's S-IC first stage. The ruptured tank would spill RP-1 onto the pad, then the oxidizer tank located above it would rupture and mix liquid oxygen with the burning fuel, triggering an explosion. They added that "the residual fire and extreme heat of the fireball [would] prevent approach to the ground area enveloped by the fireball for an unknown period."
References:
Estimation of Fireball from Saturn Vehicles Following Failure on Launch Pad, NASA Program Apollo Working Paper No. 1181, R. High and R. Fletcher, NASA Manned Spacecraft Center, Houston, Texas, 3 August 1965.
